module adder(cout,sum,a,b,cin);
output cout;
output[3:0] sum;
input[3:0] a,b;
input cin;
	adder_1bit f0(cin1,sum[0],a[0],b[0],cin);
	adder_1bit f1(cin2,sum[1],a[1],b[1],cin1);
	adder_1bit f2(cin3,sum[2],a[2],b[2],cin2);
	adder_1bit f3(cout,sum[3],a[3],b[3],cin3);
endmodule


